Metathesis is a catalytic reaction that involves the interchange of alkylidene units among compounds containing one or more double bonds (e.g., olefinic compounds) via the cleavage and formation of carbon-carbon double bonds. Metathesis may occur between two like molecules (often referred to as “self-metathesis”) and/or it may occur between two different molecules (often referred to as “cross-metathesis”). Self-metathesis may be represented schematically as shown below in Equation (A):Ra—CH═CH—Rb+Ra—CH═CH—Rb↔Ra—CH═CH—Ra+Rb—CH═CH—Rb,   (A)wherein Ra and Rb are organic groups.
Cross-metathesis may be represented schematically as shown below in Equation (B):Ra—CH═CH—Rb+Rc—CH═CH—Rd↔Ra—CH═CH—Rc+Ra—CH═CH—Rd+Rb—CH═CH—Rc+Rb—CH═CH—Rd,   (B)wherein Ra, Rb, Rc, and Rd are organic groups. Self-metathesis will also generally occur concurrently with cross-metathesis.
In the case of natural oil-derived polyenes, such as dienes or trienes, metathesis may occur at any one of the two or more carbon-carbon double bonds, typically separated by a methylene group. Without selectivity toward the terminal or internal double bonds, a metathesis of such compounds can lead to complex mixtures of a wide range of different compounds. In many cases, reaction at the internal carbon-carbon double bond is preferred, as that reaction may result in the creation of certain particularly stable co-products (such as 1,4-cyclohexadiene), which can end up acting as thermodynamic sinks. In such cases, it can be difficult to obtain reasonable yields of the longer-chain metathesis products that would be obtained if reaction at the terminal carbon-carbon double bonds were preferred.
Therefore, there is a continuing need to discover methods that can generate higher yields of products formed through reaction of the terminal carbon-carbon double bonds of polyenes.